Hi @mjb646,
The simplest way I can think of to do this would be using Discussions. You can create a discussion and enable liking so studends could vote. Students can attach or embed their image in a discussion post they create. There are a couple things that may not work exactly how your original vision was though... First, you mentioned grading (I'm not sure if you meant the context of giving points in the gradebook or not), and while you could make the discussion graded and assign points, discussions wouldn't auto-grade based on anything. Second, there wouldn't be a way to limit students to a single like/vote, so they could in theory like every single image, but as a practical matter I don't think many would do that and there'd still likely be a pretty clear winner with more likes than the others.
Perhaps others will have some additional suggestions for you too!
-Chris